It could be the plastic tube as well, mine leaks up near the wipers. I think the I.D was 3.5 mm.
Same here. Previous owner change the tube with thicker one but shorter
, and when is cold (below zero), the tube is shrinking in length and pops out from wiper. I have also problems with front screen washer pump. In the rear I have the necessary flow for a decent wash of the screen.
I have disassembled the 2in1 pump (front + rear washer) and the valves seems to work properly.
I will wait to warm outside to solve the problem.
Respect